1. Field of the Invention
The present invention relates to an ink jet recording apparatus that records an image with a recording head discharging ink drops from nozzles, and a method and a program for checking the condition of the nozzles.
2. Description of the Related Art
In ink jet recording apparatuses, when the ink jet recording apparatus records an image received from, for example, a host computer (hereinafter referred to as “received image”), a state in which some nozzles of the recording head do not discharge ink drops (hereinafter referred to as “non-discharge”) can occur. This non-discharge is caused by adhesion of ink in the nozzles, clogging in the nozzles due to dust or bubbles, or problems with heaters in the nozzles. In addition, a state in which some nozzles discharge ink drops in inappropriate directions (hereinafter referred to as “oblique discharge”) can occur. This oblique discharge is caused by ink or dust adhering around the discharging ports of the nozzles, or lack of discharging power due to deterioration of heaters in the nozzles. Moreover, a state in which initial discharge of some nozzles is defective and discharging velocity is inappropriately low (hereinafter referred to as “defective initial discharge”) can occur. This defective initial discharge is caused by defective transfer of discharging energy due to deterioration of the nozzles.
If the non-discharge, oblique discharge, or defective initial discharge occurs, the recording apparatus cannot record an image accurately. Therefore, before performing recording of the received image, the recording apparatus checks the nozzles, that is to say, checks whether normal discharge, non-discharge, oblique discharge, or defective initial discharge will occur. If non-discharge, oblique discharge, or defective initial discharge is detected, an appropriate maintenance processing is carried out. In this way, the recording apparatus can always record an image accurately.
In the process flow for recording a received image, first, an initial processing is carried out and then the nozzles are checked. If no defective nozzles are detected, a recording sheet is fed, and the received image is recorded on it. Thereafter, the recording sheet is ejected, and image recording is completed. If any non-discharge, oblique-discharge, or defective-initial-discharge nozzles are detected, purgative processing (e.g., sucking ink out of the nozzles) or maintenance processing (e.g., error processing) is carried out.
For example, Japanese Patent Laid-Open No. 2003-276171 discusses a system for checking nozzles. The system includes a plurality of detecting units. Each detecting unit includes a light-emitting device and a light-receiving device. The light-emitting device emits an optical beam. The light-receiving device receives the optical beam. The plurality of detecting units are disposed so that an ink drop discharged from a nozzle of a recording head crosses and intercepts the optical beams. The plurality of detecting units are arranged parallel to the direction in which an ink drop is discharged. This system can detect not only non-discharge but also inappropriate discharge. That is to say, the system has a plurality of pairs of light-emitting/receiving devices that are disposed just below a row of nozzles and arranged vertically and parallel to each other. On the basis of whether a discharged ink drop intercepts the optical beams, the system can detect non-discharge and inappropriate discharge (in direction or velocity).
However, since the above system needs at least two pairs of light-emitting/receiving devices, the above system is expensive and occupies much space. In addition, the first pair of light-emitting/receiving devices nearest to the ink-discharging surface of the recording head, where the discharging ports of the nozzles are provided, need to be disposed at a distance from the ink-discharging surface so that the optical beam between the light-emitting/receiving devices does not come into contact with the ink-discharging surface. Therefore, in the case of oblique discharge, if the deviation angle is large, the discharged ink drop does not intercept the first optical beam, and the system mistakes the oblique discharge as non-discharge.